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LibJS: Add basic support for "continue" in the bytecode VM

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Unlike the convoluted unwind-until-scope-type mechanism in the AST
interpreter, "continue" maps to a simple Bytecode::Op::Jump here. :^)

We know where to jump based on a stack of "continuable scopes" that
we now maintain on the Bytecode::Generator as we go.

Note that this only supports bare "continue", not continue-with-label.
This commit is contained in:
Andreas Kling 2021-06-06 13:33:02 +02:00
parent 79eac08f5b
commit 4bdfe73895
4 changed files with 32 additions and 0 deletions
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10
Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
View file

@ -110,6 +110,7 @@ Optional<Bytecode::Register> AssignmentExpression::generate_bytecode(Bytecode::G
Optional<Bytecode::Register> WhileStatement::generate_bytecode(Bytecode::Generator& generator) const
{
generator.begin_continuable_scope();
auto test_label = generator.make_label();
auto test_result_reg = m_test->generate_bytecode(generator);
VERIFY(test_result_reg.has_value());
@ -117,13 +118,16 @@ Optional<Bytecode::Register> WhileStatement::generate_bytecode(Bytecode::Generat
auto body_result_reg = m_body->generate_bytecode(generator);
generator.emit<Bytecode::Op::Jump>(test_label);
test_jump.set_target(generator.make_label());
generator.end_continuable_scope();
return body_result_reg;
}
Optional<Bytecode::Register> DoWhileStatement::generate_bytecode(Bytecode::Generator& generator) const
{
generator.begin_continuable_scope();
auto head_label = generator.make_label();
auto body_result_reg = m_body->generate_bytecode(generator);
generator.end_continuable_scope();
auto test_result_reg = m_test->generate_bytecode(generator);
VERIFY(test_result_reg.has_value());
generator.emit<Bytecode::Op::JumpIfTrue>(*test_result_reg, head_label);
@ -209,4 +213,10 @@ Optional<Bytecode::Register> IfStatement::generate_bytecode(Bytecode::Generator&
return {};
}
Optional<Bytecode::Register> ContinueStatement::generate_bytecode(Bytecode::Generator& generator) const
{
generator.emit<Bytecode::Op::Jump>(generator.nearest_continuable_scope());
return {};
}
}

15
Userland/Libraries/LibJS/Bytecode/Generator.cpp
View file

@ -47,4 +47,19 @@ Label Generator::make_label() const
return Label { m_block->instructions().size() };
}
Label Generator::nearest_continuable_scope() const
{
return m_continuable_scopes.last();
}
void Generator::begin_continuable_scope()
{
m_continuable_scopes.append(make_label());
}
void Generator::end_continuable_scope()
{
m_continuable_scopes.take_last();
}
}

6
Userland/Libraries/LibJS/Bytecode/Generator.h
View file

@ -29,6 +29,11 @@ public:
Label make_label() const;
void begin_continuable_scope();
void end_continuable_scope();
Label nearest_continuable_scope() const;
private:
Generator();
~Generator();
@ -37,6 +42,7 @@ private:
OwnPtr<Block> m_block;
u32 m_next_register { 1 };
Vector<Label> m_continuable_scopes;
};
}